Prior to the present invention, various types of forming equipment and processes have been developed for quantity production improvements to shape blanks of metallic materials into a wide range of items. Among such equipment and processes are super and quick plastic forming dies and processes in which a ductile sheet of superplastic metal alloy is heated and stretched onto the forming surfaces of heated dies to produce high-quality, light-weight parts such as panels for automotive vehicles. Often such sheets are quite large so that trunk lids, engine hoods or other large panels can be formed in one piece. Examples of such processes and equipment are found in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Sanders et al for Superplastic Forming Process and U.S. Pat. No. 5,819, 572 issued Oct. 13, 1998 to P. E Krajewski for Lubricating System For Hot Forming, both assigned to the assignee of this invention and both hereby incorporated by reference.
In the patent to Sanders et al. a blank sheet of metal alloy is heated to a superplastic forming temperature and is pulled over and around a forming insert in a die set. Subsequently using differential gas pressure, the sheet is further stretched into conformity with a forming surface of the insert so that thinning of the formed part is minimized. In the patent to Krajewski, dry lubricant is applied to a metallic sheet which is subsequently heated to predetermined forming temperatures and formed into a part in superplastic forming die equipment. The lubricant initially provides improved forming of the part and subsequently improved release of the formed part from the forming die.
Formed part removal is further addressed in copending patent application Ser. No. 09/837,597 filed Apr. 19, 2001 by R. Kleeber et al for Panel Extraction Assist for Super and Quick Plastic Forming Equipment assigned to the assignee of this invention and hereby incorporated by reference. In the above-identified application, forming pressures used for making superplastic parts in hot forming dies are further employed for improved ejection of the part from the forming die.
While the above identified patents and patent application constructions provide improvements in super and quick plastic forming they often do not attain new and higher standards for the production of such formed parts with minimized part rejection from part distortion resulting from part ejection forces. More particularly with some equipment, difficulties have been experienced in quantity production in accurately positioning the blanks or sheets onto the forming die and then subsequently removing the formed part or panel without distortion or other damage from release or ejection forces.
The employment of guide pins and cooperating guide pin slots for the forming die and blank sheet respectively to precisely position the blank sheet on the forming die has only met with limited success in view of the fact that the material of the blank expands or otherwise distorts during the forming process and grips onto the guide and positioning pin. This gripping inhibits removal of the formed panel from the die. Often the formed panel is distorted to such an extent by the part ejection forces moving the part from the pin and the associated forming die that the panel has to scrapped and recycled. FIG. 4 of the accompanying drawings illustrates prior art panel distortions from the panel being held to the forming die by the guide pin and in response to ejection forces being applied to remove the panel.